ANDROID: trusty: fix compiler warnings for 32-bit builds

On arm32, the call to min() in trusty_share_memory() uses types
size_t and unsigned long, which fails the strict type checking and
causes a compiler warning.  Use min_t(size_t, ...) instead.

Also in trusty_share_memory(), on arm32 the value of smc_ret.r3 isn't
correctly used when building ffa_handle.  This causes a
-Wshift-count-overflow compiler warning, but it appears to be an actual
bug as well.  Fix it.

Change-Id: I981088646d97baef57f85688ae0159574ed6dfe8
Signed-off-by: Eric Biggers <ebiggers@google.com>